Method of purifying textile materials



,called continuous process.

Patented Dec. 2, 1941 METHOD OF PURIFYING TEXTILE MATERIALS Louis S.Fryer, Harvey A. Schwartz, and Emerson B. Helm, Cleveland, Ohio,assignors to Industrial Rayon Corporation, Cleveland, Ohio, a

corporation of Delaware No Drawing. Application March 12, 1940,

Serial No. 323,630

11 Claims.

This invention relates to the purification of textile materials; i. e.,fabrics, threads, filaments, fibers, etc., of which some or all of thecomponent elements have been produced by the viscose process.

In the viscose process, the thread is formed by the extrusion of asolution of sodium cellulose xanthate (viscose) into an aqueouscoagulating bath which contains sulphuric acid, together with certain ofitsmetallic salts. By the action of the coagulating bath, the cellulosecontent of the viscose is regenerated, so that the resulting thread ismade up largely of hydrated cellulose. Sulphur is formed in 'and uponthe thread by the regeneration reaction, in consequence whereof itusually becomes necessary to desulphurize it. If it is desired toproduce a particularly lightcolored or white product, a bleachingoperation is performed to eliminate organic and even some inorganicimpurities which tend to give the thread an undesirable color.

In the prior art, either or both of these purification operations may beperformed separately upon the thread; either or both, upon the fabricformed of the thread; or one may be performed upon the thread and theother upon the fabric. Similarly, the desulphurizing and bleachingoperations may be performed upon the thread either in the course of oneof the usual discontinuous processes of manufacturing thread; e. g.,upon thread in skein form, or as a part of the so- Although difieringfrom the prior art in respects hereinafter to be pointed out, thepresent invention embraces to the same extent as the prior art thesealternative ways of performing the operations in question.

In the after-treatment of freshly spun multiple filament viscoseartificial silk thread, it is the usual procedure to wash the threadthoroughly to free it of acid and then desulphurize it by subjecting itto the action of an alkaline desulphurizing liquid; e. g., sodiumsulphide. The thread is then washed free of desulphurizing medium, afterwhich it is usually bleached. In the ordinary case, the bleachingtreatment is followed by an anti-chlorination treatment to remove anyresidual bleaching material which, in time. might damage the thread;thereafter, the thread is once again washed and finally dried.

A similar sequence of operations has been followed heretofore inprocessing fabrics; that is, the fabric is desulphurized, washed free ofthe desulphurizing agent, bleached, subjected to the action of ananti-chlorination agent, and washed again before being dried.

According to one embodiment of the present invention, previouslyuntreated material; e. g., thread still wet with acid carried therewithfrom the coagulating bath, is subjected first to a bleaching operationand then to a desulphurizing operation without interposing any washing,antichlorination or drying steps between the bleaching anddesulphurizing operation. The one and only washing operation performedupon the material may be, and preferably is, deferred until after thebleaching and desulphurizing operations have been completed. Ifdesulphurization is not desired, the material may be bleached and driedwithout the intervention between the bleaching and drying operations ofa Washing operation, an anti-chlorination operation or both.

The preferred procedure is to bleach freshly spun multiple filamentviscose artificial silk thread soon after its formation, desulphurize itimmediately after performance of the bleaching operation, and wash itafter the desulphurization operation has been completed. Such preferredprocedure makes it possible to eliminate at least two washingtreatments, performing the remaining washing treatment only after thethread has been bleached and desulphurized. This procedure not onlyresults in economies made possible by the elimination of the usualwashing operations, but, notwithstanding the omission of steps formerlyconsidered necessary, gives rise to a thread of superior physical andphysico-chemical properties.

In the practice of the invention, the bleaching agent may convenientlybe a halite, preferably a chlorite, of a metal selected from a classcomprising -the alkali and alkaline-earth metals. For example, anaqueous solution of sodium chlorite (NaClO2) rendered somewhat acidic bythe addition of a weak organic acid such as acetic acid; i. e., having ahydrogen ion concentration corresponding to a value of pH 5 or less,constitutes a satisfactory bleaching medium. Efficient bleaching actionis obtained by'the use of such a bleaching medium even if the materialbeing bleached is a freshly formed thread which has not been washed freeof the acid carried over by the thread from the coagulating bath.

After being bleached in a solution of this type. the material is notsubjected to an anti-chlorination treatment or washing, but is subjectedimmediately to a desulphurizing treatment. A dilute alkaline solution ofsodium sulphite (NazSOz) will be found to act very satisfactorily;however. other desulphurizing media which may be employed are solutionsof alkali or alkaline-earth rial is desulphurized immediately afterbleaching without intermediate treatment, no harmful results occur whenit is desulphurized, not withstanding the fact that it is subjected tothe action of an alkaline desulphurizing liquid while still containingthe residual acidic bleaching liquid.

Once the material being treated has been bleached and desulphurized, itmay be washed free of desulphurizing liquid, after which it may bedried. For these purposes, washing and drying operations of the ordinarykind may be employed. The resulting product is whiter and has a morepleasing appearance than that obtainable if sodium hypochlorite isemployed for bleaching as in prior purification practices. The tensilestrengths are equal to or greater than those of materials treated byprior practices, es-

pecially those in which desulphurization precedes bleaching of thematerial.

Although the invention may be practiced in various ways, preferredmethods are given in the following examples:

Example I In the spool-spinning process of making multiple filamentviscose artificial silk thread, viscose is extruded into a coagulatingbath containing approximately 8% H2504, Na2SO4, and 1% 211804. on aspool which, after it has been filled, is placed in a wash box of theconventional kind. Air is drawn into the interior of the spool throughthe package of thread for a period of approximately five minutes. Thethread on the spool in the wash box is then bleached by subjecting itfor three hours to treatment by a sodium chlorite bleaching solutionheated to about 60 C.

The bleaching solution preferably comprises a .3% aqueous solution, byweight, of commercial sodium chlorite. The latter is a flaky,crystalline, whitish powder comprising, by weight, NaClOz 83.4%, M101031.9%, NaCl 6.8%, NaOH 2.7 and H 5.2%. The acidity of the solution isadjusted to pH 3.3 with acetic acid before it is employed to bleach thethread. The NaClOz,

the active bleaching constituent, yields a high proportion of availablechlorine as compared with most bleaching agents and yet does notdeleteriously afiect the tensile strength of the treated material.

At the end of the three-hour period, the bleaching solution is drainedfrom the wash box, after which air is again drawn through the threadpackage for approximately five minutes. The package of thread on thespool is then treated in the same wash box for a period of two hourswith a .5% aqueous solution of sodium sulphite maintained atapproximately 60 C. During this period, the rather considerable amountof sulphur remaining in the thread after completion of the bleachingoperation is taken may be dried; The drying opera'tioniis performed. we9m wa hi th ihr e ie vw The thread is collected in package form2,265,033 sulphides, sulphites and silicates. If the matethe spool. Thedried thread is characterized by a clear white color and an extremelylow sulphur content; indeed, the sulphur content runs well below .05%,based on the dry weight of the thread. The thread also has excellenttensile properties and dyeing qualities.

Example II Fabric formed of unbleached, undesulphurized thread is boiledfor one hour in an aqueous solution comprising .1%, by weight, of thebleaching agent described in Example I, which solution has previouslybeen rendered acid (in this case, to pH 3.0-3.5) by the addition ofacetic acid. The

ratio of weight of solution to weight of cloth is preferably 25 to 1.After such boiling, the fabric is squeezed to remove excess bleachingliquid and is then subjected for two hours to treatment with a .5%solution of sodium silicate at 30 C., whereby it is desulphurized. Thefabric is then washed for the first time for one hour with water at C.Thereafter th bleached desulphurized cloth is dried in the usual manner.The resulting fabric is characterized by a pleasing white color, lowresidual sulphur content, and excellent physical properties.

Potassium bromite, potassium iodite, sodium bromite, sodium iodite,potassium chlorite, cal cium chlorite, barium chlorite and similarhalites of the alkali and alkaline-earth metals may be regarded asequivalents of the sodium chlorite employed as the preferred bleachingagent in the foregoing examples of the practice of the presentinvention. Any suitable desulphurizing agents of the types alreadymentioned may be used in place of the particular desulphun'zing agentsindicated in the examples; however, other alkaline solutions of alkalior alkaline-earth sulphides, sulphites or silicates; e. g., potassiumsulphide, calcium sulphide, barium sulphide, potassium sulphite, calciumsulphite, barium sulphite, potassium silicate, ammonium sulphite, andammonium sulphide, may be employed as desulphurizing agents.

The processes outlined above and described in the foregoing examples maybe modified in various ways. As described or modified, they may beapplied to the processing of materials other than those described. Ingeneral, they may, without departing from the spirit of the invention,be applied to any product of which part or all of the component elementshave been made by the viscose process. It is intended that the patentshall cover, by suitable expression in the appended claims, whateverfeatures of patentable novelty reside in the invention.

What is claimed is:

1. The method of purifying textile material comprising the steps ofbleaching said material by treating it with an aqueous solution ofsodium chlorite acidified with acetic acid; desulphurizing said materialbefore the bleaching solution is washed therefrom, the desulphurizingstep being performed by treating said material with an alkali-aqueoussolution of sodium silicate; washing the desulphurizing solution fromsaid material; and drying said material.

2. In a process of purifying textile material involving the steps ofbleaching and desulphurizing the material, the method comprisingtreating the material with an acid-aqueous solution of a bleachingsubstance and, after completion of the bleaching treatment, treating thematerial with an alkali-aqueous solution of a desulphurizing substancewithout applying a washing treatment intermediate the bleaching anddesulphurizlng treatment.

3. In a process of purifying textile material involving the steps ofbleaching and desulfurizing the material, the method comprisingbleaching the material with an aqueous solution of a halite of ametalfrom the group consisting of alkali and alkaline earth metals, saidsolution'being acidified with a weak acid; treating the material with analkali-aqueous solution of a desulfurizing substance before thebleaching substance has been washed therefrom; washing the desulfurizingsubstance from the material; and drying the material.

4. The method set forth in claim 2 wherein the desulfurizing substanceis sodium silicate.

5. The method set forth in claim 2 wherein the desulfurizing substanceis a sulfide of a metal selected from a group consisting of alkali andalkaline-earth metals.

6. The method set forth in claim 2 wherein the desulfurizing substanceis a sulfite of a metal selected from a group consisting of alkali andalkaline-earth metals.

'7. In a process of purifying a fabric formed of artificial silk threadwhich has been coagulated in an acidic medium involving the steps ofbleaching and desulfurizing the fabric, the method comprising treatingthe fabric with an acidaqueous solution of a bleaching substance and,after completion of the bleaching treatment, treating the fabric with analkali-aqueous solution of a desulfurizing substance, the desulfurizingtreatment being performed without washing the fabric in the meanwhile.

'8. In a discontinuously performed process of purifying artificial silkthread which has been coagulated in an acidic medium involving the stepsof bleaching and desulfurizing the thread,

the method comprising treating the thread with an acid-aqueous solutionof a bleaching substance without employing a washing treatment followingthe step of forming the thread and, after completion of the bleachingtreatment, treating the thread with an alkali-aqueous solution of adesulfurizing substance without washing the thread between the bleachingand desulfurizing treatments, the thread being in batch form at the timewhen the treating steps are performed upon it.

9. The method set forth in claim 2 wherein the bleaching substance is ahalite of a metal selected from a group consisting of alkali andalkaline-earth metals.

10. The method set forth in claim 2 wherein the bleaching substance issodium chlorite.

11. In a process of purifying continuous fila ment viscose artificialsilk thread which has been coagulated in an acidic medium involving thesteps of bleaching and desulfurizing the thread, the method comprisingtreating the thread with an acid-aqueous solution of a bleachingsubstance without employing a washing treatment following the step offorming the thread; treating the thread after the bleaching treatmentwith an alkali-aqueous solution of a desulfurizing substance withoutwashing the thread intermediate the bleaching and desulfurizingtreatments; treating the thread with a washing substance for the purposeof washing the desulfurizing substance from the thread; and drying thethread, the thread being in continuous filament form up to and includingthe time when the drying step is performed upon it.

LOUIS S. FRYER. HARVEY A. SCHWARTZ. EMERSON B. HELM.

